Fluorocarbon resins, in particular vinylidene fluoride resins, are endowed with outstanding mechanical properties within a broad range of temperature, excellent resistance to high temperature, organic solvents and to various chemically aggressive environments.
Thanks to their properties, they are commonly used for manufacturing articles by extrusion or injection molding, e.g. for producing pipes, tubes, fittings, films, coatings, cable sheathings, flexible pipes and the like.
In particular, off-shore pipelines such as those used to pump oil and gas ashore from off-shore drilling rigs and terminals are required to be capable of withstanding very high internal pressures and temperatures and are therefore typically made of metals such as iron and steel.
However, among major issues encountered with steel pipelines in general and off-shore pipelines in particular is the problem of corrosion.
In order to protect the inner bore of the pipelines from the corrosive effects of materials passing through them, such as mixtures of hydrocarbons, water and other contaminants, e.g. carbon dioxide and hydrogen sulphide, it has been already proposed to provide a liner made of a suitable polymeric material.
In order to be able to install a liner in an existing steel pipeline, the liner either needs to be considerably under-sized with respect to the pipeline, in which case the long term stability and integrity of the liner would be compromised, or the liner needs to be capable of being installed in a contracted form and then expanded to full or nearly full size to fit with the pipeline.
High density polyethylene has long been used for liners in land-based pipelines carrying mains water. However, polyethylene is not suitable for use in harsh chemical environments.
Polyvinylidene fluoride (PVDF) has also been proposed as a liner material for hydrocarbon pipelines on account of its resistance to hydrocarbons and other associated pipeline fluids at temperatures of up to 130° C. or more.
For instance, multilayer pipes are known in the art which are suitable for use as liners in off-shore oil and gas pipelines such as those described in GB 2318399 (GLYNWED PIPE SYSTEMS LIMITED) 22 Apr. 1998, said multilayer pipes comprising a barrier layer formed from a first polyvinylidene fluoride material and a structural layer formed from a second polyvinylidene fluoride material, the barrier layer being thinner than the structural layer.
Also, US 2005/0229992 (E.I. DU PONT DE NEMOURS AND CO.) 20 Oct. 2005 discloses a process for lining the interior surface of a pipe for conveying chemicals, especially an oil pipe, wherein a tubular line made from a fluoropolymer, said tubular line having an outer diameter greater than the interior diameter of the pipe, is mechanically reduced, inserted in the pipe and expanded into tight engagement with the primer layer or barrier layer, if present, of the interior surface of the pipe. Non-limitative examples of fluoropolymers suitable for manufacturing the tubular liner include, notably, PVDF homopolymers and blends of PVDF homopolymers with acrylic polymers.
Further, pipes made of blends of vinylidene fluoride (VDF) based polymers are described in EP 1375588 A (ATOFINA CHEMICALS INC.) 2 Jan. 2004 which are notably suitable for use as pipe liners with improved stress resistance. However, no mention is made therein of a process for lining or relining pipelines wherein the pipe liner is installed in a contracted form and then expanded to its full or nearly full size to fit with the pipeline.
There is thus still a need in the art for a solid-wall pipe liner endowed with suitable mechanical properties to be successfully installed in oil and gas metal pipelines in a contracted form and then expanded to its full or nearly full size to fit with the pipeline, without cracking or fracturing of the pipe, while being resistant to heat and pressure and to harsh chemical environments in the long term.